Current technologies used for long-term tissue stimulation employ electrodes, leads and devices, all of which being implantable. For example, in order to stimulate cardiac tissue for treatment of bradycardia, implantable pacemaker systems use up to three electrodes deployed in the heart via appropriate leads. The leads connect to the header of the pacemaker can, which is implanted, typically, in a skin pocket located in the left or right chest. The leads are threaded through a vein, typically a subclavian vein, into the superior vena cava. Depending on the pacemaker configuration, one lead and its electrode are positioned in the high right atrium, a second lead in the right ventricle, and a third lead, if used, in one of the coronary sinus branches that extends over the epicardial aspect of the left ventricle. The pacemaker can carries a set of integrated circuits and a battery. Given the low power consumption of its electronic circuits, a typical pacemaker is expected to last between 7-10 years, after which the battery typically has been depleted. The patient would have to undergo a surgery to have the pacemaker replaced.
While highly effective in treating bradycardia, implantable pacemakers can have adverse effects, mostly related to lead fractures, infections of the skin pocket, premature battery depletion, software upgrades, etc. Particularly, in older patient population the leads can cause significant wear and tear of neighboring tissue layers. Similarly, the skin pocket associated with the pacemaker can is, in certain patient populations, very prone to infections, edema or hematoma. If the battery depletes sooner than expected, the patient would have to be exposed to early surgery to have the device replaced. In case of problems with the software that runs inside the pacemaker, patients may also have to undergo surgery to have the device replaced (certain pacemaker models still run their code from ROM memory, rather than RAM, which makes it very problematic to perform software upgrades without resorting to device replacement via surgery).
In recent years, given the large number of older patients that wear pacemakers, compatibility with magnetic resonance imaging (MRI) systems has become desired. It is important to note that even the modern pacemaker models do not perform their functions per specifications when the patient is placed in the vicinity of MRI equipment. In most cases, the pacemaker has to be turned off. If the patient is pacemaker-dependent special solutions have to be employed to keep their heart paced during the MM procedure. Additionally, the MRI fields can generate significant heating in the leads or around the can. Such heating can cause inadvertent thermal tissue damage.
Implantable stimulator systems are currently used for many other applications. Stimulation of the nerves system is, for example, another area of application. Patients may wear devices that perform spine stimulation, vagus nerve stimulation or brain stimulation. All such devices currently on the market use leads to connect the stimulating electrodes to the controller that drives them.